Datasheet

4–14
4.6 CycleMark
The format of the CycleMark data is shown in Figure 4–20 and is described in Table 4–8. The receiver
module inserts a single quadlet to mark the end of an isochronous cycle. The quadlet is inserted into the
GRF.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
Reserved
ReservedReserved
CyDne
Figure 4–20. CycleMark Format
Table 4–8. CycleMark Function
FIELD NAME DESCRIPTION
CyDne The CyDne field indicates the end of an isochronous cycle.
4.7 PHY Configuration Transmit
The transmit format of the PHY-configuration packet is shown in Figure 4–21 and described in Table 4–9.
The PHY-configuration packet contains three quadlets, which are loaded into the ATF. The first quadlet is
the tCode for an unformatted packet. This is written into ATF_First at address 80h and has a value of
0000_00E0h. The second quadlet consists of actual data. This is written into the ATF_Continue at address
84h and has a value of the first quadlet of the PHY-configuration packet. The third quadlet is the logical
inverse of the second quadlet and it written into the ATF_Continue&Update at address 8Ch and has a value
of the second quadlet of the PHY-configuration packet.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
1110000000000000
logical inverse of first 16 bits of first quadlet
root_ID gap_cnt
00
RT
0000000000000000
1111111111111111
0000000000000000
Packet
Identifier
tcode=E
Figure 4–21. PHY-Configuration Packet Format
There is a possibility of a false header error on receipt of a PHY-configuration packet. If the first 16 bits of
a PHY-configuration packet happen to match the destination identifier of a node (bus number and node
number), the TSB12LV01B on that node issues a header error since the node misinterprets the
PHY-configuration packet as a data packet addressed to the node. The suggested solution to this potential
problem is to assign bus numbers that all have the most significant bit set to 1. Since the all-ones case is
reserved for addressing the local bus, this leaves only 511 available unique bus identifiers. This is an artifact
of the IEEE 1394–1995 standard.
The PHY-configuration packet can perform the following functions:
• Set the gap-count field of all nodes on the bus to a new value. The gap-count, if set intelligently,
can optimize bus performance.
• Force a particular node to be the bus root after the next bus reset.
It is not valid to transmit a PHY-configuration packet with both the R bit and T bit set to zero. This would cause
the packet to be interpreted as an extended PHY packet.